<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>less</title>
    <style>
        html{
            /*css支持变量的设置*/
            --color:yellow;
            --length:200px;
        }
        .box1{
            width:var(--length);
            height:200px;
            /*背景颜色*/
            background-color:yellow;
        }
        .box2{
            /*calc()计算函数*/
            width:calc(200px*2);
            height:100px;
            /*字体颜色*/
            color:red;
            font-size: 50px;
        }
        .box3{
            width:100px;
            height:100px;
            /*边框颜色*/
            border:10px solid var(--color);
        }
    </style>
</head>
<body>
    <div class="box1">aaaaa</div>
    <div class="box2">aaaaa</div>
    <div class="box3">aaaaa</div>
    
</body>
</html>